The present invention relates to telemetry in general and, more particularly, to a plurality of cooperating telemetry systems.
In certain types of radio systems there exist many battery operated transmitters that periodically transmit short duration messages to one or more receivers. One example of such systems are telemetry systems, another example is burglary and fire alarm systems that can also be viewed as a specific telemetry system. In these systems, many transmitters located at different places transmit messages indicative of the status of monitoring sensors to a telemetry receiving station (e.g., a receiver with a processor that collects the data from the sensors, etc.). Usually the transmitters include a battery status and sometimes also the temperature in the transmitted messages in addition to the monitored sensor status. Normally, the transmitters transmit supervisory status messages that are as short as feasible and the period between the transmissions is as long as feasible in order to minimize the average current drain from the battery. In addition, short and infrequent transmissions lower the probability that the data is lost due to collisions which occur when two or more transmitters transmit at the same time. However, when an alarm or an abnormal condition occurs, a transmitter transmits immediately in order to convey the alarm message with little delay.
In order to identify the sensors, each associated transmitter is numbered and identified by a transmitter identification number (identification) number. Usually, such a system has one telemetry receiving station that receives data from the transmitters. Typically, the telemetry receiving station has to convey unusual system status to a central monitoring facility that collects data from several systems that are often placed in different geographical locations.
The illustrative embodiment of the present invention comprises a plurality of telemetry systems where each system comprises several remote telemetry transmitters to intermittently transmit short duration messages indicative of the status of the sensors associated with the transmitters, and at least one telemetry collection unit having a radio transceiver. In an illustrative embodiment of the present invention, the telemetry collection units forward alarm messages received from other telemetry collection units and respond to messages from remote telemetry transmitters associated with other telemetry collection units. In effect, the telemetry collection units and the associated remote telemetry transmitters form a meshed wireless telemetry system in which telemetry collection units cooperate with each other in order to increase reliability and lower the cost of each system. Such meshed telemetry system can communicate with a remote central monitoring station via one or more network interface units connected to a private or public wired or wireless network. In an illustrative embodiment, the network interface unit is wireless equipment that connects to one telemetry collection unit. In accordance with an illustrative embodiment, there are fewer wireless network interface units than there are telemetry collection units in the meshed system, thus, in a meshed system, the cost of the wireless network interface unit can be shared between several telemetry systems. However, in an alternative embodiment the network interface unit is a wireline modem, and there may be one modem for each telemetry system.
In accordance with an illustrative embodiment, the telemetry system has the telemetry collection unit receiver augmented by a transmitter circuitry thus rendering it to become a system transceiver. Such a modification is simple and inexpensive since the transmitter can share most of its circuits with receiver. For example the transmitter control can be accomplished by the same logic circuit or microprocessor as the receiver. Also some of the radio frequency circuits such as the synthesizer and reference frequency can be reused.
In accordance with an illustrative embodiment, the telemetry collection unit receives messages from the remote telemetry transmitters that are associated with this telemetry collection unit and it is responsive to the received messages. In addition, the telemetry collection unit receives and is responsive to the messages transmitted by remote telemetry transmitters associated with other telemetry collection units. In an illustrative embodiment, the telemetry collection unit has the identification numbers of the transmitters associated with this telemetry collection unit. In addition, in the illustrative embodiment, in operation, the telemetry collection unit is furnished with identification numbers of remote telemetry transmitters that are associated with other telemetry collection units and that are to be monitored by this telemetry collection unit. In the illustrative embodiment, such furnishing is accomplished by exchanging information and cooperation with the other telemetry collection units.
In an illustrative embodiment, the telemetry collection units from different systems communicate with each other and exchange information to obtain mutual coverage of their respective transmitters. In operation, telemetry collection units of two systems establish communications with each other and exchange information about the remote telemetry transmitters that belong to each system. This may include transmitter identification and signal quality of the received messages. Based on the exchanged information, the telemetry collection units can agree to receive and be responsive to the messages received from the remote telemetry transmitters that belong to the other system.
In accordance with an illustrative embodiment, the telemetry collection units from different systems communicate with each other and exchange information in order to pass along alarm (or other) messages until they reach a terminating node, i e. a wired or wireless network interface unit or a telemetry collection unit that is coupled to or equipped with a wired or wireless network interface unit. In accordance with an illustrative embodiment there are fewer network interface units than there are telemetry collection units, thus making it possible to share one network interface unit between several systems. However, in an alternative illustrative embodiment there is one network interface unit for each telemetry system. E.g. in a burglary alarm application, each system is equipped with a wireline modem that is vulnerable to an attack by cutting the phone line. In such case, the telemetry collection unit of the system under attack can sent an alarm information to a central monitoring facility by communicating with another telemetry collection unit that belongs to another system. This way reliability is improved without an expense of a wireless interface unit.
In accordance with an illustrative embodiment, in operation, the telemetry collection unit (receiver) receives messages from the various remote telemetry transmitters, some of which may require that the central monitoring facility be notified. When such a message is received, the telemetry collection unit transmits a message that is directed to a telemetry collection unit from other system. Ordinarily, this is the nearest telemetry collection unit. Upon reception and confirmation, the message is passed along in a similar way to the next telemetry collection unit. If the confirmation is not received, the message may be retransmitted a predetermined number of times. Similarly, the message is passed from one telemetry collection unit to the next until it reaches the final destination that is: a wired or wireless network interface unit or a telemetry collection unit coupled to or equipped with a wired or wireless network interface unit. In effect, the telemetry collection units form nodes in a network through which the messages are routed from the source to the destination,i.e. the terminating node. At any point along the way the message is routed, the path selected by a telemetry collection unit can be altered as needed, e.g. if the nearest telemetry collection unit is not operative, an alternative route can be selected. Preferably, the alternative paths are selected on the basis of the signal quality and distance to the terminating node, wherein the signal quality is measured along the entire selected path to maximize the transmission reliability.
Similarly, in accordance with an illustrative embodiment messages are carried in reverse direction; i e. from network interface unit to a telemetry collection unit.
In accordance with an illustrative embodiment, in some cases it may be preferable that the messages are broadcasted (rebroadcasted) instead of routed. In such a case, the originating node broadcasts the first message, then each telemetry collection unit that received the message retransmits (rebroadcasts) the message, thus making it possible for the message to reach many nodes of the system. In a way, the message floods the network thus ensuring that at least one terminating node receives the message. The message may be rebroadcasted by each node a predetermined number of times, or alternatively, rebroadcasting stops when the confirmation message is received from the terminating node.
Similarly, in accordance with an illustrative embodiment messages are carried in reverse direction; i.e. from network interface unit to a telemetry collection unit.
In accordance with an illustrative embodiment, each remote telemetry transmitter transmits short duration messages at predetermined time intervals in such a way that each transmitter transmits each consecutive message at a different frequency. For each remote telemetry transmitter, the frequency variations are selected according to a sequence, and the sequence is determined individually for each transmitter based on the transmitter identification number. The frequency sequences are orthogonal, a coincidence of frequencies at one time excludes the coincidence at any other time for the duration of the entire sequence. This way, the possibility is eliminated that two or more remote telemetry transmitters interfere with each other during more than one message transmission for the duration of the entire sequence. In addition, transmission at varied, i e. diverse, frequencies reduces probability that all transmitted messages are lost due to interference or signal fading that are predominantly frequency selective.
Alternatively, in accordance with an illustrative embodiment, each remote telemetry transmitter can vary the time between transmissionsxe2x80x94TBTxe2x80x94according to a predetermined pattern. Preferably, for each remote telemetry transmitter, the pattern of variations depends on the transmitter identification number. This way, the possibility is eliminated that two or more remote telemetry transmitters interfere with each other during more than one message transmission for the duration of the entire sequence.
In accordance with another illustrative embodiment, the remote telemetry transmitters vary both the frequency and time between transmissions in order to maximize the system reliability. In this way, the receiver is relived from the burden to receive more than one message at different frequencies at the same time. Thus, the receiver circuit complexity is reduced. Preferably, the frequency-time sequences are orthogonal.
In accordance with an illustrative embodiment, the transmitters in the telemetry collection units perform similar periodic transmissions and frequency and time variations as the remote telemetry transmitters as described above.